Stabilized viscous mineral oil composition



P'atented Feb. 24, 1942 UNITED STATES PATENT OFFICE STABILIZED VI-SCOUS IHINERAL OIL COMPOSITION No Drawing. Application November 22, 1939, Serial No. 305,674

15 Claims.

This invention has to do with the stabilization of viscous mineral oil fractions against the harmful effects of oxidation. It is more particularly related to the improvement or stabilization of viscous mineral oils such as turbine oils, transformer oils and internal combustion engine lubricants by the use of addition agents which when admixed with the oil in minor proportions will prevent or delay those undesirable changes which normally take place under conditions of use.

As is well known to those familiar with the art, substantially all of the various fractions obtained from mineral oils are susceptible to oxidation. This susceptibility of an oil fraction to oxidation and the manner in which the oxidation manifests itself within the oil varies with the oil fraction, viscous oils such as lubricants and dielectrics being distinguished from non-viscous fractions such as gasoline and kerosene. It also varies with the type and degree of refinement to which the oil fraction has been subjected and the conditions under which the oil is used or tested. In-other words, the products formed in a mineral oil fraction as a result of oxidation and the degree to which they are formed under given conditions depends upon the chemical character of various unstable constituents or constituents which may act as oxidation catalysts in a particular fraction. It naturally follows that the formation of the undesirable oxidation products in a refined viscous oil is dependent upon the extent to which the constituents which tend toward their formation have been removed by refining operations.

A highly refined viscous oil, for example, which is one that has been refined by treatment with filming sulfuric acid or other means or combinations such as AlCla, solvents, and acids (or with large quantities of concentrated sulfuric acid), tends to form relatively large amounts of acidic constituents when subjected to oxidizing conditions. The presence of catalytic materials such as copper does not appear to appreciably affect the oxidation of highly refined oils, and such oils are less prone to the formation of colored bodies or of insoluble sludge. The formation of acidic bodies, however, is highly undesirable for most applications of these oils. For example, when used as an insulating or cooling oil in electrical equipment such as transformers or capacitors, an increase in acidic bodies tends to lower the dielectric strength of the oil and has other harmful effects which are undesirable. The acids are corrosive to metals'and thus reduce the useful life of the" oils as lubricants or for other purposes in which they come in contact with metals, and the acidic materials are also im'urious in textile lubricants and in spray oils.

Moderately refined oils-that is, oils that have been refined by treatment with only moderate amounts of sulfuric acid or other refining agentstend to form relatively small amounts of acidic oxidation products, as compared with highly refined oils, but they undergo material color depreciation and form considerable amounts of sludge. The changes taking place in these oils are appreciably accelerated by the presence of metal catalysts such as copper. Sufiicient acid is generally formed to cause some reduction in the dielectric strength of these oils, but the principal objection to them is their tendency to deposit sludge which interferes with heat transfer in transformers and turbines and also causes plugging of oil feed lines in lubricating systems.

Solvent-refined oils in general, which have been prepared by treatment with selective solvents such as chlorex, phenol, furfural, etc., resemble the moderately refined acid-treated oils in that their oxidation is accelerated by the presence of metals such as copper and further in that it is attended by substantial color depreciation and sludge formation. Acid formation is usually greater than in the case of moderately acid-refined oils but considerably lem than with highly refined oils. Both sludge and acid formation lower their value for many purposes such as electrical insulation, lubrication, etc. Also, solventrefined oils have found extensive use as lubricants for internal combustion engines because of their high viscosity index, but under the conditions of use encountered in crankcases such oils develop constituents which are corrosive toward certain metal bearings such as the cadmium-silver bearing, etc, which are sometimes used.

It is to be understood that this classification is by no means limiting and that there can exist viscous mineral oils whose refining and blendin has been such as to make them intermediate in properties between the types set up. Thus, response to inhibitors may be said to depend entirely upon the type of oxidation and end products of oxidation of an oil, which in turn depends largely upon the degree of refining this oil has had. Further, the degree of refining required to produce these types of oils varies with the crude source so that any one refining procedure may produce either a highly refined oil or a moderately refined oil, depending on the crude source. Pennsylvania type oils, for example, re-

' phenyl paraphenylene diamines.

quire much less refining to produce highly refined oils than the Coastal type of oils.

The use of oxidation inhibitors for the purpose of stabilizing a viscous mineral oil fraction against the deleterious effects of oxidation discussed above is well known. Since the action. of these inhibiting materials is apparently catalytic, the problem of their development is a difficult one and is evidently influenced to a large degree by the oxidizable constituents which are in the oil following a particular refining treatment. Thus, a particular inhibitor or class of inhibitors may be effective to stabilize a highly refined oil against acid formation while the same inhibitor may have no appreciable effect upon acid, color or sludge formation in a moderately refined oil and vice versa. This same inhibitor may or may not be effective in inhibiting acid,

oil and may or may not be effective to inhibit the corrosive action of a solvent-refined oil toward metals such as used in" cadmium-silver bearings. Furthermore, the behavior of an insludge, and color formation in a solvent-refined hibitor in a non-viscous mineral oil fraction does not necessarily afford any indication as to what its effect will be in a viscous oil fraction.

The present invention is predicated upon the discovery that the class of compounds herein broadly referred to as N-aryl phenylene diamines or more specifically as N-phenyl phenylene diamines is highly effective in stabilizing viscous mineral oil fractions of the class hereinabove referred to against the deteriorating effects of oxidation. One outstanding feature of the com-- pounds contemplated herein as inhibitors for viscous oils is that the compounds are effective in inhibiting the effects of oxidation upon a viscous oil fraction irrespective of the refining treatment which the oil has had. This is an imspecific subgroup of compounds is a substituted or unsubstituted phenyl radical. The term phenyl as used herein is intended to include both substituted and unsubstituted phenyl radicals, the preferred group of substituted phenyl radicals being those in which the phenyl nucleus carries one or more alkyl substituents. Illustrative of the phenyl radical R in the general formula above are the unsubstituted phenyl radicals and substituted phenyl radicals, such as methylphenyl, ethylphenyl, propylphenyl, butyl-- phenyl, amylphenyl, dimethylphenyl, trimethylphenyl, etc.

As indicated above, this invention contemplates the general class of N-phenyl phenylene diamines as inhibitors of oxidation in viscous oils. This general class of compounds includes the'N-phenyl orthophenylene diamines, the N- phenyl metaphenylene diamines,' and the N- In the examples given hereinafter, the effectiveness of the compounds contemplated herein is illustrated with the N-phenyl paraphenylene diamines, and special preference is given herein to these para compounds, which have the general formula:

in which R represents a substituted or unsubstituted phenyl radical.

In general, the compounds described herein may be synthesized by methods well known to those skilled in the art and at least one of these compounds, N-phenyl paraphenylene diamine, is available in commerce as the acid salt.

As has been previously indicated, it is an outstanding feature of these N-phenyl paraphenyl Highly refined oils The oils used in this test was. one suitable for use in transformers which had been prepared by treating a Coastal distillate with 40 pounds of 98 per cent sulfuric acid and 180 pounds of 103 per cent oleum per barrel, followed by washing and clay percolation. It had a specific gravity of 0.871, a flash point of 310 F., and a Saybolt Universal viscosity of 69 seconds at F. This type of oil tends to form acidic products on oxidation. The test used involved heating a sample of the oil or oil blend to a temperature of C. and bubbling oxygen therethrou'gh for a period of '70 hours. The acidic products thus formed were determined by titrating with alcoholic potash and were reported as neutralization number or N. N. values. The results obtained from this oil alone and oil blends containing characteristic N-phenyl paraphenylene diamines are set forth in' Table I below.

Table I Per N. N. Inhibitor cent values,

None 25.0 N-phenyl paraphenylene (iiamine 10 0.0 N-p-methyl phenyl paraphyenylene diamine 10 0.0

EXAMPLE Two Moderately refined oils The oil used in this test was a mixed Mid-Continent and Coastal distillate which had been refined by treatment with 70 pounds of 98 per cent sulfuric acid per barrel, neutralized, washed.

At varying time intervals the samples were tested for acidity, color, and sludge, the results obtained with the oil alone and with oil blends containing representative compounds of the type contemplated herein being set forth in Table II below.

Table 11 Per Time, Lov. Sludge Inhibitor cent hours color mg./25 cc.

None 72 14 6 68 168 .99 26 17 240 2. 110 336 16. 0 400 1, 282 N -phenyl paraphenylene diamine 500 0.0 280 21 1, 004 0. 0 160 16 o 1,-508 39 18 11 N-p-metlhyl l pheiiyl parap any one amine 10 310 01 275 483 02 300 838 01 316 1, 152 0 310 EXAMPLE Tnasa Solvent refined oils The oil used in this test was a distillate from a Rodessa crude which had been refined with furfural, dewaxed, and filtered. It had a specific gravity of 0.856, a flash point of 420 F., and a Saybolt Universal viscosity of 151 seconds at 100 The oil was tested by the same procedure outlined in Example Two above, and the results obtained from the oil alone and characteristic N-phenyl paraphenylene diamines are set forth in Table m below.

Exam: Form Corrosion test As has been previously indicated, motor oils, especially those refined by certain solvent-extracftion methods, tend to oxidize under the conditions of use encountered in internal combustion engines andthrough such oxidation form prodnote which corrode certain bearing metals, particularly certain of the hard metal alloys such as the cadmium-silver alloys and other alloy metals having the corrosion susceptibility of cadmiumsilver alloys. The present invention contemplates internal combustion engine lubricants of thetype which are normally corrosive to such bearing metals but in which this corrosive action has been inhibited by the addition to the oil of an N-phenyi paraphenylene diamine. The invention also contemplates a method of lubricating internal combustion engine bearing surfaces of the type above referred to, which method involves maintaining the initial edective lubricating properties of the oil without its normally developedcorrosive action by incorporating in the oil film an N-phenyl paraphenylene diamine in an amount suflicient to retard the corrosion. The effectiveness of the compounds contemplated herein as inhibitors of the corrosive action just discussed was demonstrated by the following test, which is used to determine the corrosive action of a motor oil on an automobile connecting rod hearing.

The oil used consisted of Pennsylvania neutral and residuum stocks separately refined by means of chlorex and then blended to given an S. A. E. No. 20 motor oil with a specific gravity of 0.872, a flash point of 435 F., and a Saybolt Universal viscosity of 318 seconds at 100 F. The oil was tested by adding a section of a bearing containing acadmium-silver alloy surface andweighing about 6 grams and heating it to 175 C. for 22 hours while a stream of air was bubbled against the surface of the bearing. The loss in weight of the bearing during this treatment measures the amount of corrosion that has taken place. A sample of the oil containing a stabilizer was run at the same time as a sample of the straight oil and the loss in weight of -the bearing section in the inhibited oil can thus be compared directly with the loss of the section in the uninhibited oil. The results obtained are set forth in Table IVbelow.

Table IV P Mg. loss in weight er- Inhibitor cent Inhibited Uninhibited N-phenyl paraphenylene diamine 25 0 62 N-p-methyl phenyl paraphenylene diamine. 25 l 85 It will be observed from the foregoing examples and the results set forth therein that the N-phenyl paraphenylene diamines are uniformly effective in inhibiting the deleterious eflects of oxidation upon viscous mineral oil fractions which have been subjected to the various meth- Ode of refining treatment currently used. In other words, these compounds are effective as inhibitors in highly refined oils, moderately refined oils and solvent-refined oils. These compounds may be used in amounts varying from about .01 per cent 'to about 1.0 per cent, but in general amounts in the neighborhood of 0.10 per cent .will give satisfactory results.

We claim:

1. An improved mineral oil composition comprising a viscous mineral oil fraction normally subject to deterioration under oxidizing conditions and in admixture therewith a minor proportion, sufilcient to retard said deterioration, of an N-phenyl phenylene diamine.

2. An improved mineral oil composition comprising a viscous mineral oil fraction normally subject to deterioration under oxidizing conditions and in admixture therewith a minor proportion, sufflcient to retard said deterioration, of an N-phenyl orthophenylene diamine.

3. An improved mineral oil composition comprising a viscous mineral oil fraction normally subject to deterioration under oxidizing conditions and in admixture therewith a minor proportion, suflicient to retard said deterioration, of an N-phenyl metaphenylene diamine.

4. An improved mineral oil composition comprising a viscous mineral oilfraction normally subject to deterioration under oxidizing condi tions and inadmixture therewith a-minor proportion, suflicient to retard said deterioration, of an N-phenyl paraphenylene diamine.

5. An improved mineral oil composition comprising a viscous mineral oil fraction normallysubject to deterioration under oxidizing conditions and in admixture therewith a minor proportion, suflicient to retard said deterioration, of a compound having the general formula portion, sufiicient to retard said deterioration,

of'a compound having the general formula in which R represents a radical selected from the group consisting of a phenyl radical and alkyl-substituted phenyl radicals.

'7. An improved mineral oil composition comprising a viscous mineral oil fraction normally subject to deterioration under oxidizing conditions and in admixture therewith a minor proportion, from about .01 per cent to about 1.0 per cent, of a compound having the general formula in which R represents a radical selected from the group consisting of a phenyl radical and alkyl-substituted phenyl radicals.

8. An improved mineral oil composition comprising a viscous mineral oilfraction normally subject to deterioration under oxidizing conditions and in admixture therewith a minor proportion, suificient to retard said deterioration, of a compound selected from the group consisting of N-phenyl paraphenylene diamine and N-alkyl phenyl paraphenylene diamines.

9. An improved mineral oil composition comprising a viscous mineral oil fraction normally subject to deterioration under oxidizing conditions and in admixture therewith a minor proportion, suflicient to retard said deterioration, of N-phenyl paraphenylene diamine.

10. An improved mineral oil composition comprising a viscous mineral oil fraction normally subject to deterioration under oxidizing conditions and in admixture therewith a minor pro-' portion, sufficient to retard said deterioration, of N-p-methyl phenyl paraphenylene diamine.

11. An improved mineral oil composition comprising a viscous mineral oil fraction, normally subject to deterioration under oxidizing conditions and in admixture therewith a minor proportion, from about .01 per cent to about 1.0 per cent, of a compound selected from the group consisting of N-phenyl paraphenylene diamine and N-alkyl phenyl paraphenylene diamines.

12. An improved mineral oil composition comprising a .viscousmineral oil fraction, normally subject to deterioration under oxidizing conditions, and in admixture therewith a minor proportion, from about .01 per cent to about 1.0 per cent, of N-phenyl paraphenylene diamine.

13. An improved mineral oil composition comprising a viscous mineral oil fraction, normally subject to deterioration unde'r'oxidizing conditions, and in admixture therewith a minor proportion, from about .01 per cent to about 1.0 per cent, of N-p-methyl phenyl paraphenylene diamine.

14. An improved mineral oil composition comprising a viscous mineral oil selected from the group consisting of transformer oils, turbine oils and internal combustion engine lubricants normally subject to deterioration under conditions of use and in admixture therewith a minor proportion, suflicient to retard said deterioration of an N -phenyl paraphenylene diamine.

15. An improved mineral oil composition comprising a viscous mineral oil fraction normally subject to deterioration under oxidizing conditions and inv admixture therewith a minor proportion, suflicient to retard said deterioration, of an N-aryl phenylene diamine.

LYLE A. HAMILTON. .EVERETT W. FULLER. 

